Abstract
For joining metallic materials for battery applications such as copper and stainless steel, laser beam micro welding with beam sources in the near-infrared range has become established in recent years. In laser beam micro welding, spatial power modulation describes the superposition of the linear feed motion with an oscillating motion. This modulation method serves to widen the cross-section of the weld seam as well as to increase the process stability. Temporal power modulation refers to the controlled modulation of the laser power over time during the welding process. In this paper, the superposition of both temporal and spatial power modulation methods is presented, which enables a variable control of the weld penetration depth. Three weld geometries transverse to the feed direction are part of this investigation: the compensation of the weld penetration depth due to the asymmetric path movement during spatial power modulation only, a W-shaped weld profile, and a V-shaped. The weld geometries are investigated by the bed on plate weld tests with CuSn6. Furthermore, the use of combined power modulation for welding tests in butt joint configuration between CuSn6 and stainless steel 1.4301 with different material properties is investigated. The study shows the possibility of precise control of the welding depth by this methodology. Depending on the material combination, the desired regions with maximum and minimum welding depth can be achieved by the control of local and temporal power modulation on the material surface.
Highlights
Energy storage systems are gaining importance due to the increasing trend of electrification, especially the stationary application as intermediate storage for power generation from renewable energies and electromobility devices
To protect the sensitive joining partners, a defined weld geometry is crucial in order not to damage the cell and at the same time to guarantee a large cross-section for the electrical current flow [5]
The aim of this work is to investigate the feasibility of influencing the weld geometry during laser beam micro welding by means of combining spatial and temporal power modulation
Summary
Energy storage systems are gaining importance due to the increasing trend of electrification, especially the stationary application as intermediate storage for power generation from renewable energies and electromobility devices. Copper bonds are suitable for cell contacting due to their high electrical and thermal conductivity but cannot be processed in conventional ultrasonic joining due to their high thermal conductivity [3]. Laser beam micro welding offers a highly automatable, contactless joining method whereby copper bonds can be processed. Compared to conventional welding processes, the intensity of the energy input is increased by focusing the laser beam down to several 10 μm in diameter to precisely weld materials with high thermal conductivity [4]. To protect the sensitive joining partners, a defined weld geometry is crucial in order not to damage the cell and at the same time to guarantee a large cross-section for the electrical current flow [5]. In the event of fluctuations or deviations in the welding depth, underlying material such as polymer substrates or electrolytes in battery storage systems can be destroyed
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